Over the past several decades, highly sophisticated techniques have been developed for identifying and producing hydrocarbons, commonly referred to as oil and gas, from subsurface formations. These techniques facilitate the discovery, assessment, and production of hydrocarbons from subsurface formations.
Downhole fluid analysis (DFA) is an important and efficient investigative technique typically used to ascertain the characteristics and nature of geological formations having hydrocarbon deposits. DFA is used in oilfield exploration and development for determining petrophysical, mineralogical and fluid properties of hydrocarbon reservoirs. In particular, DFA may be used to analyze the properties and phase behavior of downhole fluids which, in turn, may be used to characterize hydrocarbon reservoirs.
Typically, a complex mixture of fluids, such as oil, gas, and water, is found downhole in reservoir formations. The downhole fluids, which are also referred to as formation fluids, have characteristics or properties including pressure, live fluid color, dead-crude density, gas-oil ratio (GOR), among other fluid properties, that may be used to characterize hydrocarbon reservoirs.
To evaluate and test underground formations surrounding a borehole, it is often desirable to obtain samples of formation fluids for purposes of characterizing the fluids. Tools have been developed which allow samples to be taken from a formation in a logging run or during drilling. The Reservoir Formation Tester (RFT) and Modular Formation Dynamics Tester (MDT) tools provided by Schlumberger are examples of sampling tools for extracting samples of formation fluids for analysis at the surface.
Recent developments in DFA include techniques for characterizing formation fluids downhole in a wellbore or borehole rather than or in addition to analysis at the surface. Specifically, Schlumberger's MDT tool may include one or more fluid analysis modules, such as the Composition Fluid Analyzer (CFA) and Live Fluid Analyzer (LFA), to analyze downhole fluids sampled by the tool while the fluids are still downhole.
In DFA modules of the type mentioned above, formation fluids that are to be analyzed downhole flow past sensor modules, such as spectrometer modules, which analyze the fluids by near-infrared (NIR) absorption spectroscopy, for example. Co-owned U.S. Pat. Nos. 6,476,384 and 6,768,105 are examples of patents relating to the foregoing techniques, the contents of these patents are incorporated herein by reference in their entireties. Formation fluids also may be captured in sample chambers associated with the DFA modules, having sensors, such as pressure/temperature gauges, embedded therein for measuring fluid properties of the captured formation fluids.